The studies proposed here are aimed at clarifying the neuronal circuitry underlying the autonomic and neuroendocrine functions of the hypothalamus in the rat and monkey. In one series of experiments, a comprehensive survey of the efferent connections of the hippocampus, septum and hypothalamus will be completed. The efferent pathways and terminal fields of the dorsomedial nucleus, supramammillary region and posterior hypothalamic area will be defined autoradiographically, and neuronal subpopulations giving rise to these pathways will be analyzed with retrograde transport methods. A similar analysis of the midbrain reticular formation, which receives massive inputs from the hypothalamus, will also be carried out. In another series of experiments, the connections of the paraventricular nucleus will be studied in detail, since it is directly related to the posterior pituitary, brainstem and spinal autonomic cell groups, and the central adrenergic system. These studies will include the following: 1) the fine structure of oxytocin-stained endings of the paraventriculo-spinal tract in the intermediolateral column will be examined with immunocytochemical methods in the rat and monkey; 2) the distribution and number of oxytocin- and vasopressin-stained cells will be quantitatively compared in male and and female rats and monkeys; 3) the relationship between the paraventricular nucleus and cell bodies of the central adrenergic system will be studied with double labeling methods using retrogradely transported fluorescent tracers injected into the paraventricular nucleus and other sites including the hippocampus and spinal cord; and 4) possible sprouting of paraventricular fibers to the external lamina of the median eminence following adrenalectomy will be studied with autoradiographic and immunohistochemical methods.